Updating value of a nested dictionary in Python - dictionary

Question

I have a nested dictionary
users={'user502':{'firstname':'James' , 'lastname':'Jones'}}
User can search for first or last name and be able to update to something else. I wrote the following code:
name_change=input('Enter name to change: ')
for key,value in users.items():
for k,v in value.items():
if name_change==v:
#print('name found in', value.get(name_change))
#print('name found in', value.get(k))
print('name found in', k)
updated_name=input('What would be the new name: ')
users.update(k=updated_name)
break
else:
print('name not found')
I am getting RuntimeError: dictionary changed size during iteration error. I did some research on update and also looked at this stackoverflow discussion Update value in nested dictionary - Python
I am not able to figure out how to point the code to pick first name or last name based on whatever user enters. Some hints would be helpful.
Thanks in advance.
**From other discussion it seems like in Python 3 it does not work because of '3.x because keys returns an iterator instead of a list.'
I tried to do a pop first and then update
updated_name=input('What would be the new name: ')
# users[k][v]=updated_name
x= value.get(k)
users.pop(x)
users[x]=updated_name
However now I get KeyError: 'James'

Answer 1

This code is doing what I wanted. May be my question was not clear sorry about that
print('Actual-', users)
name_change=input('Enter name to change: ')
for key,value in users.items():
for k,v in value.items():
if name_change==v:
#print('name found in', value.get(name_change))
#print('name found in', value.get(k))
print('name found in', k)
updated_name=input('What would be the new name: ')
value[k]=updated_name
break
else:
print('name not found')
print("modified name:", users)
Output:
Actual- {'user502': {'lastname': 'Jones', 'firstname': 'James'}}
Enter name to change: Jones
name found in lastname
What would be the new name: January
modified name: {'user502': {'lastname': 'January', 'firstname': 'James'}}